Analysis Number
1292048
Petrology Number
TS30864
Historical Petrology Number
P396/73
Analyst
Petrology Analysis Date
Thin Section in Storage
Y
Petrology Specimen Type
Thin Section
Lithology
Unclassified Igneous
Summary Decription
Sheared and altered basic igneous rock
Detailed Decription
Rock Name:
Sheared and altered basic igneous rock
Hand Specimen:
A dense, dark grey-green rock
Thin Section:
An optical estimate of the constituents gives the following:
Chlorite 30-40%
Green amphibole 10-15%
Sericite 35-40%
Plagioclase 5%
Epidote Trace
Opaques 2-3%
This rock appears to represent a basic igneous rock similar to the New Well dolerite which, prior to alteration, contained pyroxene and plagioclase as its main constituents. The primary minerals have been extensively replaced and the igneous texture largely destroyed by micro-shearing. The original pyroxene has been replaced chiefly by green chlorite and where it has been replaced by bluegreen uralitic amphibole,the original pyroxene cleavage is locally preserved. Most of the plagioclase has been completely sericitized; however, some lath like pseudomorphous shapes and fresh grains are still present, which testify to its igneous origin. Several of the laths are fractured and strained due to the shearing stresses.
A few small granular aggregates of epidote have developed, probably by replacement of the plagioclase. Opaques have been remobilized and occur as short, wavy stringers along the micro-shear planes through the rock.
Weathering has caused minor iron oxide-staining of the chlorite.
This rock, therefore, is very probably an altered and deformed, tholeiitic microgabbro or dolerite, very similar to that at New Well.
Mineral Abundances by Volume
Abundant > 70%
Major 30-70%
Chlorite, Sericite
Minor 5-29%
Amphibole, Plagioclase
Trace 1-4%
Opaque mineral
Rare <1%
Epidote
Unknown abundance
Rock Sample Petrology information pending.